The present invention generally relates to lithography, and in particular to reflective reticles for use in extreme ultraviolet (EUV) lithography for printing a pattern onto a device such as a wafer or a circuit board.
In the semiconductor industry, there is a continuing trend toward higher device densities. To achieve these high densities there has been and continues to be efforts toward scaling down the device dimensions on semiconductor wafers. In order to accomplish such high device packing density, smaller features sizes are required. This may include the width and spacing of interconnecting lines.
The requirement of small features with close spacing between adjacent features requires high resolution lithographic processes. In general, projection lithography refers to processes for pattern transfer between various media. It is a technique used for integrated circuit fabrication in which a silicon slice, the wafer, is coated uniformly with a radiation-sensitive film, the resist, and an exposing source (such as light, x-rays, or an electron beam) illuminates selected areas of the surface through an intervening master template, the mask, for a particular pattern. The lithographic coating is generally a radiation-sensitized coating suitable for receiving a projected image of the subject pattern. Once the image is projected, it is indelibly formed in the coating. The projected image may be either a negative or a positive of the subject pattern. Exposure of the coating causes the image area to become selectively crosslinked (for a negative projection) or deprotected (for a positive projection) and consequently either more or less soluble (depending on the coating) in a particular solvent developer. The more soluble (i.e., uncrosslinked or deprotected) areas are removed in the developing process to leave the pattern image in the coating as less soluble polymer.
Projection lithography is a powerful and essential tool for microelectronics processing. As feature sizes are driven smaller and smaller, optical systems are approaching their limits caused by the wavelengths of the optical radiation. A recognized way of reducing the feature size of circuit elements is to lithographically image them with radiation of a shorter wavelength. xe2x80x9cLongxe2x80x9d or xe2x80x9csoftxe2x80x9d x-rays (a.k.a, extreme ultraviolet (EUV)), wavelength range of lambda=50 to 700 Angstroms (xc3x85) (5 to 70 nm) are now at the forefront of research in an effort to achieve the desired smaller feature sizes.
EUV lithography may be carried out as follows. EUV radiation is projected onto a resonant-reflective reticle. The resonant-reflective reticle reflects a substantial portion of the EUV radiation which carries a pattern for an IC layer formed on the reticle to an all resonant-reflective imaging system (e.g., series of high precision mirrors). A demagnified (optically reduced) image of the reticle pattern is projected onto a resist-coated wafer. The entire reticle pattern is exposed onto the wafer by synchronously scanning the reticle and the wafer (i.e., a step-and-scan exposure).
Although EUV lithography provides substantial advantages with respect to achieving high resolution patterning, errors may still result from the EUV lithography process. For example, defects on the reticle may cause defects in corresponding locations on the wafer. These defects on the reticle may be difficult and costly to correct. The corresponding defects on the wafer may also be difficult or even impossible to correct, with the difficulty of correcting mistakes generally increasing as device density on the wafer is increased. Uncorrectable mistakes in the reticle or wafer result in decreased performance, increased costs, and/or scrapping of products.
Additionally, EUV masks or reticles are increasingly expensive to fabricate, with costs projected to be in excess of $100,000 each. Since reticles generally involve a permanent image etched or otherwise formed into reflective material, a new IC design or change to an existing IC design involves production of a new mask or reticle design.
Consequently, it will be appreciated that it would be desirable to have a reticle that could be used to form various patterns, and that would minimize the impact of defects.
The present invention involves a programmable reticle having a plurality of addressable pixels. Each of the pixels has one or more elastic elements which underlie a reflective surface, the elements each being activatable for selectively deforming part of the reflective surface. The amount of deformation is such that light reflected from a deformed part destructively interferes with light reflected from the vicinity of the deformed part.
The programmable reticle may be used as a part of a scanning lithography system wherein a wafer or other device to be exposed is moved to expose different of its areas, while the pattern on the programmable reticle is changed to reflect the desired exposure pattern of the area of the wafer currently being exposed. In such a scanning system, any given point on the wafer will be exposed using a number of different pixels on the reticle; therefore the effect of a defective pixel will be xe2x80x9cdilutedxe2x80x9d or xe2x80x9cvoted outxe2x80x9d by the other, non-defective pixels also involved in exposing that spot.
According to one aspect of the invention, a programmable reflective lithography reticle includes a substrate; a plurality of addressable pixels on the substrate, each of the pixels having at least one activatable elastic element; and a reflective material for reflecting light incident on the reticle. The elements selectively locally displace portions of the reflective material, thereby causing destructive or constructive interference of light reflected by the reflective material in the vicinity of the elements.
According to another aspect of the invention, a lithography system includes a light source; a reflective reticle reducing optics for focusing light emitted from the reticle on a wafer; and a scanning mechanism for moving the wafer to expose different areas of the wafer to light emitted from the reticle. The reticle includes a substrate; a plurality of addressable pixels on the substrate, each of the pixels having at least one activatable elastic element; and a reflective material for reflecting light incident on the reticle. The elements selectively locally displace the reflective material, thereby causing destructive or constructive interference of light reflected by the reflective material in the vicinity of respective of the elements; and
According to a further aspect of the invention, a method of making a programmable lithography reflective reticle includes the steps of: forming bottom electrodes on a substrate; depositing a layer of piezoelectric material on top of the bottom electrodes and the substrate; depositing a top electrode layer on the piezoelectric material; and depositing a reflecting material on the reticle.
To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative embodiments of the invention. These embodiments are indicative, however, of but a few of the various ways in which the principles of the invention may be employed. Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the drawings.